1. Field of the Invention
The present invention relates to surgical devices and methods for adjusting tension of ligament grafts. The invention has particular utility in connection with establishing ligament graft tension in knee surgery applications, and will be described in connection with such utility, although other utilities are contemplated.
2. Description of the Prior Art
Treatment of knee instability due, for example, to rupture of the anterior cruciate ligament has been a mixture of ligament repair, augmentation or substitution by tendon transfer. The most common technique at the present time is the use of an autogenous patella tendon graft with bone harvested from the patella and the tibial tuberosity. The patella tendon graft and bone plugs are fed into tunnels within the femur and tibia and secured at each end.
Successful tendon graft surgery is dependent on several factors including graft selection, tunnel placement, isometric placement, bone preparation, fixation devices, correct tensioning of the graft, and post-surgical rehabilitation, all of which have been thoroughly studied. All of the above factors are highly critical, and any variation from optimal control can result in graft failure. By way of example, theoretically, isometric placement is possible where the ligament remains at the same tension throughout the range of knee flexion and extension. However, this is difficult to achieve in practice. Many recent developments have attempted to define the isometric points for insertion of the drill and have demonstrated the effect of incorrect placement.
For the ligament to be functional, it not only has to be inserted isometrically, but it has to be correctly tensioned in order to allow a full range of motion. Various techniques have been developed for determining correct graft tensioning during a patella tendon reconstruction, none of which have been completely satisfactory since existing techniques do not permit measurement through full range of motion. In particular, excessive graft tension has been found to be detrimental to success in a continuous passive motion. Any graft material that is highly tensioned will be more subject to abrasion at the bony edges of tunnels or the notch and also subject to more frequent fixation failure. Thus, the importance for correct tensioning. Moreover a significant variable that has received little attention is the precise preloader tension applied to the graft before fixation. Another technical problem is to ensure that once proper tension on the graft is set, that the tension is maintained, without change, during fixation of the ends of the this ligament. Moreover, no method is believed to be currently available which permits tension to be incrementally increased while the range of motion and stability is continuously examined.
It is, accordingly, an object of the present invention to provide the system, i.e. method and apparatus which overcomes the aforesaid and other disadvantages of the prior art. Another object of the present invention is to provide the method and apparatus which is uniquely suited for establishment of proper skeletal referenced ligament graft tension. It is a specific object of the invention to provide a method and apparatus for establishing proper skeletal referenced ligament graft tension and fixation of a cruciate ligament graft during knee surgery.